Problem 130 - A Complete Resource Book in Chemistry for JEE Main

Question

Which represents the correct set of reactions and test here? List I 1 . Oc1c(Br)cc(Br)cc1Br CC Oc1ccccc1 Phenol \(\quad 2,4,6\)-tribromophenol 2\. \(3 \mathrm{C}_{6} \mathrm{H}_{3} \mathrm{OH}+\mathrm{FeCl}_{3} \longrightarrow\) CC(C)(C)C \(\left(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{O}\right)_{3} \mathrm{Fe}^{3}+3 \mathrm{HCl}\) Ferric phenoxide 3\. \(\left(\mathrm{NH}_{4}\right)_{2}\left[\mathrm{Ce}\left(\mathrm{NO}_{3}\right)_{6}\right]+2 \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{OH}\) Phenol \(\left[\mathrm{Ce}\left(\mathrm{NO}_{3}\right)_{4}\left(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{OH}\right)_{2}\right]+2 \mathrm{NH}_{4} \mathrm{NO}_{3}\) Green or brown ppt. 4\. \(\mathrm{R}-\mathrm{CO}-\mathrm{CH}_{3}+3 \mathrm{I}_{2}+4 \mathrm{NaOH}\) \(\mathrm{CHI}_{3}+3 \mathrm{NaI}+3 \mathrm{H}_{2} \mathrm{O}+\mathrm{RCOONa}\) List II (i) Ceric ammonium nitrate test (ii) Bromine water test (iii) Ferric chloride test (iv) Iodoform test The correct matching is \(\begin{array}{llll}1 & 2 & 3 & 4\end{array}\) \(\begin{array}{llll}\text { (a) (ii) } & \text { (i) (iv) (iii) }\end{array}\) (b) (i) (ii) (iv) (iii) (c) (ii) (iii) (i) (iv) (d) (i) (iv) (ii) (iii)

Step-by-Step Solution

Answer

Option (c): List II matches (ii), (iii), (i), (iv) with List I (1, 2, 3, 4).

Step 1: Understand Chemical Reactions in List I

Analyze each chemical reaction in List I to determine the type of test it represents. Identify the substances and the reactions to suggest the corresponding chemical test. 1. The reaction involves a phenol and Br (bromine), which forms a tribromophenol. This is typical of a **Bromine water test**. 2. The reaction with FeCl3 forms a complex with phenol, a characteristic of the **Ferric chloride test**. 3. The reaction involves ceric ammonium nitrate with phenol, producing a green or brown precipitate, identifying the **Ceric ammonium nitrate test**. 4. The reaction with NaOH, I2, and an organic compound yielding CHI3 is known for the **Iodoform test**.

Step 2: Match Tests with Correct Sequence in List II

Based on the understanding from Step 1, match the chemical reactions to the tests listed in List II: - Reaction 1 matches with **(ii) Bromine water test**. - Reaction 2 matches with **(iii) Ferric chloride test**. - Reaction 3 matches with **(i) Ceric ammonium nitrate test**. - Reaction 4 matches with **(iv) Iodoform test**.

Step 3: Compare with Provided Options

Compare the sequence derived from the matching to the given options in the problem: The order from List I (1, 2, 3, 4) is matched with List II as **(ii), (iii), (i), (iv)**. Review the provided answer choices: - **Option (c):** (ii), (iii), (i), (iv) - matches our findings. Thus, the correct answer is option **c**.

Key Concepts

Bromine Water Test

The bromine water test is a simple yet effective chemical reaction in organic chemistry, used specifically to test for unsaturation such as alkenes and phenols. When bromine, which is a brownish-red liquid, is added to an organic compound, you might notice a disappearance of the color indicating the presence of an unsaturated compound. This is because bromine adds across the multiple bonds present in alkenes or reacts with phenol.

Here's what happens chemically when bromine reacts with phenol: the resulting compound, 2,4,6-tribromophenol, displays a whitish precipitate.

• The organism: bromine adds to the aromatic ring of phenol.
• Phenol's electrophilic reaction converts the solution from colorless to a cloudy suspension.

Using the bromine water test, chemists can quickly assert the presence of specific unsaturated atoms in a molecule, which is crucial for further organic compound classification.

Ferric Chloride Test

An often used test to identify phenols in organic compounds is the ferric chloride test. It leverages the unique ability of phenol to form a complex with iron(III) chloride, resulting in a color change. Typically, adding ferric chloride results in a violet, green, blue, or red color, depending on the phenol's structure.

The reaction proceeds as follows: phenol interacts with reagents like \( ext{FeCl}_3\), forming ferric phenoxide alongside other ionic compounds.

• The phenol forms a complex compound, enhancing the visible change after testing.
• It's a straightforward and highly sensitive test for phenolic functional groups.

This test is critical in laboratories for its practicality, offering a visual indication of phenolic content within a sample.

Ceric Ammonium Nitrate Test

The ceric ammonium nitrate test is designed to detect alcohol functional groups in organic compounds. The test reagent is a deep orange-yellow compound, and upon interaction with alcohol, a visible color change denotes a positive test result. For example, when phenol reacts with ceric ammonium nitrate, the solution may darken, resulting in a green or brown precipitate.

Phenol’s reaction in this test can be observed as follows:

• Reactivity: Alcohol causes an immediate color change due to complex formation with cerium ions.
• The presence of phenol results in a unique, easily identifiable precipitate.

This test is instrumental in distinguishing alcohols within a broad range of organic compounds, thanks to its rapid and distinct results.

Iodoform Test

The iodoform test is a classic method used to identify the presence of methyl ketones and secondary alcohols with a methyl group.

Let’s walk through this reaction:

• When an organic compound (for instance, acetone) reacts with iodine in an alkali medium like sodium hydroxide, you'll observe the formation of a yellow precipitate known as iodoform.
• Specifically, this test identifies methyl groups situated adjacent to a carbonyl or hydroxyl group, distinguishing it from other functional systems.

This test holds significant importance in organic chemistry, as it precisely pinpoints compounds bearing specific alkyl groups, aiding in the classification and identification of unknown substances in an analytically sound manner.